[PATCH] D117912: [IR] document and update ctlz/cttz intrinsics to optionally return poison rather than undef

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D117912#3262125 <https://reviews.llvm.org/D117912#3262125>, @efriedma wrote:

> You mean, we might reach a point where we could make clang emit is_zero_poison=false without anyone caring?  Don't think we're quite there yet.  x86-64-v2 doesn't include lzcnt.  And not sure about the current state of the compiler-rt/libgcc intrinsics.

Yes, I was wondering what level of default x86 tuning was needed to flip the setting...I suppose that's x86-64-v3 ("Close to Haswell").


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